Piezo-electric plate



May 9, 1933. A, HUND 1,908,479

PIEZO-ELECTRIC PLATE Filed May 17, 1926 INVENTOR.

f ATTORNEY Patented May 9, 1933 PATEN FFHCEIE AUGUST HUND, OF BETHESDA,ZBIARYLAND, ASSIGNOR, BY MESNE ASSIGNMENTS; TO

WIRED RADIO, INCL, OF NEH. YORK, N. Y., A CORPORATION OF DELAWAREPIEZO-ELEGTRIC PLATE Application filed May 17,

My invention relates broadly to methods of preparing piezoelectricplates and more particularly to a process for cutting and grindingpiezoelectric plates for the production of piezoelectric elementscapable of sustaining oscillations of audio frequency.

One of the objects of my invention is to provide a method for preparingpiezoelectric plates from natural quartz whereby audio frequencyoscillations may be sustained in an associated electrical circuit wherethe plate is relatively thin.

Another object of my invention is to provide a piezoelectric element ofrelatively small size which is capable of sustaining low frequencyelectrical oscillations.

A further object of my invention is to provide a piezoelectric elementwhich is so cut and ground from natural quartz that a plurality ofdiffering high frequency oscillations may be produced thereby andintegrated in .a common circuit for the development of an audiblefrequency beat note for application in a variety of different ways.

A still further object of my invention is to provide a piezoelectriccrystal element having a plurality of differing axes wherein thedifferent high frequency oscillations may be generated for theproduction of a beat frequency for securing an audible note from arelatively small size plate.

My invention will be more fully understood from the specificationhereinafter following by reference to the accompanying drawing wherein:

Fig. 1 is a perspective view of a quartz body in its natural crystallinestate showing the cutting of a piezoelectric plate therefrom in a planeparallel to the optical axis in a manner as set forth in more detail inmy U. S. Patent No. 1,822,928, issued September 15, 1931; Fig. 2 is anend View representing an end section of thenatural quartz body wherein apiezoelectric plate is cut therefrom in a plane disposed-at an angle toa plane determined by one of the Y axes and the Z axis in accordancewith the principles of my invention herein; Fig. 3 is a theoretical viewshowing the normal electrical polarization existent in a piezoelectricplate prepared in 1926. Serial NO. 109,786.

the manner illustrated in Fig. 1; Fig. 4 is a theoretical viewillustrating the electrical polarizations within a piezoelectric platewhich has been prepared in accordance with the principles of myinvention illustrated in Fig. 2; and Fig. 5 shows the arrangement of apiezoelectric plate prepared in accordance with Figs. 2 and 4 in anelectron tube circuit arranged for the generation of several differentradio frequencies and the production of a relatively low frequency beatnote.

In accordance with the conventional practice in the piezoelectriccrystal art the optic electric and crystallographic axes of the quartzcrystal from which the piezoelectric element is out are designatedrespectively by the letters Z, X and Y as illustrated in Fig. 1 of thedrawing.

A. piezoelectric plate when properly cut and ground serves to sustainoscillations in an electron tube circuit where the oscillations are of aconstant frequency and a value corresponding to a function of thethickness of the piezoelectric plate. Where the piezoelectric plate iscut and ground according to the principles set forth in myaforementioned patent only one thickness vibration is possible. Thisthickness vibration occurs along the electrical polarization axisindicated in Fig. 3 at t, which is an electrical polarization effectalong the X-axis of Fig. 1. There are three X-axes or electricalpolarization axes spaced 120 apart because of the threefold symmetry ofquartz, and I have indicated the other two of these in Fig. 3 each bythe symbol 225. The values 225 are both equal to each other and theirlength is twice as great as that of the line t. A compression wave alongthe axis 25 is therefore the first harmonic of the frequencycorresponding to that produced by a compression wave along either of theaxes 2t. A single frequency with its first harmonic is thereforeproduced which is directly related to the thickness of the plate.

I have discovered that by cutting the piezoelectric plate as representedin Fig. 2 at an angle to a plane determined by one of the Y axes and theZ axis, that three different effective polarization axes exist throughthe piezoelectric plate as represented at t t and 2? in Fig. 4 whichgenerally have no harmonic relations. By reason of the plurality ofeffective axes through the piezoelectric plate in Fig. 4 there will beseveral modes of vibration through the piezoelectric plate. By cuttingthe piezoelectric plate at an angle a to the normal cut it is thereforepossible to affect any two of the three effective thicknesses as to makethem almost alike and such as to produce an audible beat frequency whichresults in an audible beat current in circuits associated with thepiezoelectric plate. The fre uency of the other effective thickness ormo e of vibration may be so far removed from the frequencies of thefirst two efiective thicknesses or modes of vibration as not to bepulled into step with the frequencies of these two eflectivethicknesses. One of the modes of vibration may be prevented frominterfering with the other modes of vibration by roper arrangement ofthe electrical circuits In which the piezoelectric plate is connected.It is also possible to adjust the lengths along the axis t t and 25 suchthat If. and t produce one beat note and t and t another beat note and tand it a third beat note of different pitch. These different beat notesmay be effectively separated and utilized in an associated circuit bythe adjustment of the inductance and capacity values as represented inFig. 5. The method of cutting the piezoelectric plates provides a platehaving polarizations along a plurality of axes so that the plate maysustain oscillations at a plurality of different fre uencies. Theparallel planes of the faces 0 the crystal lie at an acute angle to aplane determined by one of the Y axes and the Z axis and interceptdifferent lengths along the piezoelectric axes. The lengths of thepiezoelectric axes are of such value as to individually producevibrations of a frequency above the audible range yet so related to eachother that the plate is capable of producing vibrations of a frequencywithin the audible ran e.

The piezoelectrlc plate is shown positioned between conductive plates 2and 3 which serve to connect the piezoelectric plate in circuit with theelectron tube 4. Electron tube 4 has an input circuit 5 and an outputcircuit 6. The in ut circuit 5 is shunted by means of a variable highresistance leak path 7 as illustrated. The output circuit 6 includesinductance 8 and variable capacity 9 with an audio frequency transformer10 having its primary 11 disposed in series therewith in the platecircuit, which includes high potential battery 12. The audio frequencytransformer 10 has a secondary winding 14 for delivering audio frequencycurrent to any desired work circuit.

The cathode of electron tube 4 is heated from a suitable source 15.Radio frequency 5 by-pass condenser 16 is connected in shunt with theprimary winding 11 and a high potential battery 12 or its equivalent forproviding a path of oscillation for the high frequency currents andenergy for sustaining the oscillations of the piezoelectric crystal 1.

A switch 17 is arranged for connectm the" crystal effectively across thegrid and cat ode of electron tube 4 by moving the switch 17 to terminal18, or the piezoelectric cr stal 1 ma be connected in shunt with the griand an e of electron tube 4 by closing switch 17 on contact 19 forsustaining high frequency oscillations in the tube system. The audiofrequency oscillations occur simultaneously in the electron tubecircuits and are effectively utilized through iron core audio frequencytransformer system 10.

In the process of grinding. the angles be-- tween 2t and t in Fig. 3will be equal and correspondingly the angles between t. and t,

may be ground in such manner that oscillations produced along thethickness t may have a value of 500 kilocycles, while the oscillationsgenerated along thickness 6 may have a value of 499 kilocycles. Theresultant beat frequency would be one kiloc cle.

The frequency t may be so far removed m these thicknesses that it iswithout the range of the beat frequency which it is desired to utilize.

The preparation of piezoelectric plates in accordance with my inventionherein for the production of low frequency oscillations reduces the sizeand cost of calibration apparatus to a considerable degree, and While Ihave illustrated my invention in its pre ferred embodiments I desirethat it be understood that modifications may be made and that nolimitations upon the invention are intended other than are imposed bythe scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. A piezoelectric element comprising a section cut from a naturalquartz crystal, said m element having a pair of parallel faces disposedparallel to the optical axis and at an angle to a plane defined by theoptical axis and a crystallographic axis such that the element isnaturally resonant to two fundamental frequencies which have an audiblebeat frequency relationship to one another.

2. A piezoelectric element having its electrode faces substantiallyparallel to the optic axis and disposed at an angle to one of thelateral faces of the mother crystal such that the element is naturallyresonant to two fundamental frequencies having an audible beat frequencyrelationship to one another, each of said frequencies being a functionof one of the oblique distances between said electrode faces measuredalong the X-axes, respectively.

3. A quartz piezo-electric element having its electrode facessubstantially parallel to the optic axis and disposed at an anglegreater than zero and less than thirty de grees to one of the lateralfaces of the mother crystal, said angle being such as to render theelement naturally resonant to two different frequencies having anaudible beat frequency relationship to one another.

4. A piezoelectric element having two substantially parallel facesdisposed at different angles to each of the three electrical axes of thecrystal from which said element is cut, whereby the element is maderesonant to at least two superaudible frequencies having an audiblebeat-frequency relationship to one another.

5. A piezoelectric crystal having two substantially parallel faces inwhich the dimension normal to said parallel faces is disposed atdifferent angles to each of the three electrical axes of said crystal,whereby the element is made resonant to at least two superaudiblefrequencies having an audible beat-frequency relationship to oneanother.

6. A piezoelectric vibrator comprising a plate of natural quartz havingtwo flat faces parallel to the optical axis and inclined with respect toone of the Y-axes so as to comprehend three different lengths of X-axesbetween said faces, the comprehended length of each said X-axis being afunction of one of the natural frequencies at which said vibrator isresonant and the ratios between said comprehended lengths of X-axesbeing such as to produce an audible beat-frequency between two of saidnatural frequencies.

7. A piezoelectric vibrator comprising a plate of natural quartz havingtwo flat faces parallel to the optical axis and comprehending betweensaid faces three different lengths of piezo-electric axes, said lengthsbeing so related to one another as to render said vibrator naturallyresonant to each of two fundamental frequencies between which thedifference frequency is within the range of audibility.

In testimony whereof I afiix my signature.

AUGUST HUND.

